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47-0928 QC793 2008-22647 CIP Lincoln, Don. The quantum frontier: the large hadron collider. Johns Hopkins, 2009. 172p bibl index afp ISBN 0801891442, $25.00; ISBN 9780801891441, $25.00 The Quantum Frontier provides [...]

Abstract.: An excitation function of the ground-state γ0-ray capture transition in 12C (α,γ)16O at θγ = 90� was obtained in far geometry using six Ge detectors, where the study of the reaction was initiated in inverse kinematics involving a windowless gas target. The detectors observed predominantly the E1 capture amplitude. The data at E = 1.32 to 2.99 MeV lead to an extrapolated astrophysical S factor S E1(E 0) = 90�15 keV b at E 0 = 0.3 MeV (for the case of constructive interference between the two lowest E1 sources), in good agreement with previous works. However, a novel Monte Carlo approach in the data extrapolation reveals systematic differences between the various data sets such that a combined analysis of all available data sets could produce a biased estimate of the S E1(E 0) value. As a consequence, the case of destructive interference between the two lowest E1 sources with S E1(E 0) = 8�3 keV b cannot be ruled out rigorously.

Abstact:: The elastic scattering cross sections, σ (E,θ), for the systems He+Ta and He+W have been measured at θlab=165° and E lab=76.1 keV to 3.988 MeV using targets with a thickness of a few atomic layers. The results are smaller than the results given by the Rutherford scattering law, σR(E,θ), due to the effects of electron screening and can be described by σ(E,θ)/σR(E,θ)=(1+Ue/E)−1, where U e is an atomic screening potential energy. The deduced average value, U e=28 ± 3 keV, is consistent with the Moliére- and Lenz-Jensen-models as well as electron binding energies.

Thed(d, n)3He andd(d,p)t fusion reactions have been studied at center-of-mass energies E=1.6 to 130 keV using intense beam currents from 30, 100, and 450 kV accelerators in combination with detectors in close and far geometry. The cross sesction ratio,R(E)=s(d,n)/s(d, p), approaches unity (within 2%) at low energies; thus there is no experimental evidence for the Oppenheimer-Phillips effect at subcoulomb energies. The cross sections of d(d, p)t at E?10keV show clear evidence for electron screening effects. However, the observed cross section enhancement is significantly larger than can be accounted for from available atomic physics models.

Cross section measurements of thed(3He,p)4He reaction have been extended to an energy as low asEcm=5.4 keV. The data have an improved accuracy compared with previous work and confirm the existence of electron screening. The combined analysis of the present and previous data leads to an electron screening potential ofUe=123 ± 9 eV. A similar analysis of previous data for3He(d, p)4He leads toUe=186 ± 9 eV. Both screening potentials differ due to the molecular and atomic aggregate state of the targets involved in these investigations and are significantly larger than expected from available atomic physics models, supporting the general trend in studies of electron screening.

The absolute cross section σof the d(7Li, p)8Li reaction near the Ecm=0.61 MeV resonance has been measured using a 7Li ion beam and a windowless gas target system filled with D2gas. The proton yield of the reaction and the β-delayed α-activity of the residual nuclides 8Li were observed both concurrently with the elastic scattering yield, relating σto the Rutherford scattering cross section σR. The resulting values, σ(from p) =143.6 ± 8.9 mb and σ (from 8Li) = 151 ± 20 mb, lead to a weighted mean value of σ =153 ± 6 mb (χ2= 2.26) including all available values and σ= 146 ± 5 mb (χ2= 0.05) removing some values from the data set. The consequences for the expected flux of high-energy solar neutrinos are discussed.

The fusion reactions6Li(p, a)3He,6Li(d, a)4He, and7Li(p, a)4He have been studied over the c.m. energy rangeE=10 to 1450 keV. Each reaction involved the use of hydrogen projectiles and LiF solid targets as well as Li projectiles and hydrogen molecular gas targets. In all cases the effects of electron screening on the low-energy fusion cross sections (exponential enhancement) have been observed; the effects are somewhat stronger in the case of atomicp ord projectiles compared to the case of molecularH2 orD2 gas targets. If isotopic effects on electron screening are negligible, all three reactions should exhibit the same enhancements for each set of experimental techniques. The measurements confirmed this expectation to a large extent.

The absolute cross sectionσof thed(7Li,p)8Li reaction near theEcm=0.61 MeV resonance has been measured using a7Li ion beam and a windowless gas target system filled with D2gas. The proton yield of the reaction and theβ-delayedα-activity of the residual nuclides8Li were observed both concurrently with the elastic scattering yield, relatingσto the Rutherford scattering cross sectionσR. The resulting values,σ(fromp)=143.6±8.9 mb andσ(from8Li)=151±20 mb, lead to a weighted mean value ofσ=153±6 mb (x2=2.26) including all available values andσ=146±5 mb (x2=0.05) removing some values from the data set. The consequences for the expected flux of high-energy solar neutrinos are discussed.

Abstract:: The absolute cross section σ (E) of the radiative capture reaction p(7Be,γ)8B at the center-of-mass energy E = 992 keV has been measured using a radioactive 7Be ion beam and a windowless gas target system filled with H2 gas. The 8B residual nuclides were detected with a recoil separator consisting of momentum and velocity filters and a ΔE-E detector telescope. The 8B yield was observed concurrently with the 7Be + p elastic scattering yield, relating σ(E) to the Rutherford scattering cross section. The resulting value, σ(E) = 0.41 ± 0.11 μb, leads to an S(E) factor at zero energy of S(0) = 16 ± 4 eV b, in fair agreement with recommended values.

The loss of ⁸Li recoil nuclei in ⁷Li(d,p)⁸Li has been measured using different backings and ⁷LiF target thicknesses as well as different deuteron energies. The results confirm essentially recent TRIM calculations. The losses are large (about 13%) for the combination of thin targets and heavy backings at E_d=0.80 MeV and increase with decreasing deuteron energy. The implications on the cross sections for ⁷Li(d,p)⁸Li and ⁷Be(p,)⁸B are discussed.

For an improved determination of the7Be(p, γ)8B absolute cross section, the reaction is studied in inverse kinematics. The study involves a7Be radioactive ion beam of 8.0 MeV, a windowless H2gas target, and an efficient recoil separator for the detection of the8B residual nuclides. The techniques used to produce such a beam as well as the first direct observation of8B are reported.

For an improved determination of the 7Be(p, γ)8B absolute cross section, the reaction is studied in inverse kinematics. The study involves a 7Be radioactive ion beam of 8.0 MeV, a windowless H2 gas target, and an efficient recoil separator for the detection of the 8B residual nuclides. The techniques used to produce such a beam as well as the first direct observation of 8B are reported.